As one example of devices for precisely discharging various liquid materials in constant amounts, there is known a plunger type discharge device for discharging the liquid material in constant amount from a nozzle by moving a plunger (or a piston) forwards within a metering section (or a syringe) that is filled with the liquid material. With that type of discharge device, because the liquid material is discharged in amount corresponding to a volume displaced by the plunger moving forwards, the liquid material can be stably discharged with higher precision than other types of discharge devices. For that reason, the plunger type discharge device is used in a variety of fields, such as resin molding for electronic components and injection of an electrolyte for a cell.
In the plunger type discharge device, before the liquid material is discharged, particularly when the liquid material is filled into the metering section in an empty state, an operation of filling the liquid material into the metering section is performed. Such a filling operation may often cause a situation that air bubbles are generated in the metering section with a pressure reduction attributable to backward movement of the plunger, or that air bubbles remain in some portions, such as corners not filled with the liquid material. If air bubbles are mixed in the liquid material within the metering section, an amount of the discharged liquid material is not held constant with respect to the stroke of the plunger moving forwards and the liquid material cannot be discharged in precise constant amount due to an influence of compressibility of the air bubbles.
To cope with the problem of ingress (mixing or trapping) of air bubbles, various proposals have been made up to date. For example, Patent Document 1 discloses a method of purging out air in a dispenser comprising a liquid material supply container in which a liquid material is stored, and a liquid material discharge device including a supply port connectable to an opening of the liquid material supply container, a discharge port through which the liquid material is discharged, a flow passage interconnecting the supply port and the discharge port, a plunger disposed midway the flow passage, and an opening/closing mechanism for opening and closing the supply port and the discharge port, the method comprising the step of connecting the supply port of the vertically-reversed liquid discharge device to the opening of the vertically-reversed liquid material supply container, and a step of filling the liquid material supplied from the liquid material supply container into the flow passage.
Meanwhile, Patent Document 2 discloses a syringe in which a relief hole forming a gap relative to a piston sealing member is formed in a hole bottom of the syringe, a liquid is injected through a discharge port of the syringe in a state that a piston is pushed into the relief hole, and after discharging air to the outside through the gap formed by the sealing member and the relief hole, the piston is slightly withdrawn to make sealing active to close the gap, thereby filling the liquid into the syringe without discharging the liquid to the outside.